Missing splits, missing dividends, double up splits, doubled up dividends, missing days of data, volume doesn't reflect all trades for a day, some optional corporate actions (eg. choose a cash dividend or a share dividend) both are included and adjusted in the price data, foreign currency dividends shown as USD dividends, fictional dividends, missing spinoffs, early history of the stock missing, crap security names, very late timing on corporate actions (sometimes months after the event and always 1 day delayed (pity the trader who puts on a stop to find there was a demerger event overnight). Really quite poor. The data is riddled with such errors.